Aspects of deformation processing of sheet metals.

Abstract

Aluminum alloys, particularly aluminum-magnesium alloys containing manganese as dispersoid formers, are beginning to show great promise for the automotive industry because of their superplastic potential, good post-formed tensile properties, and possible strong resistance to corrosion. Part I of this work focuses on the superplastic response and subsequent microstructural evolution of a typical Al-Mg alloy, namely 5083Al. Macroscopic forming parameters have been investigated and optimal conditions for superplasticity have been developed. Results of microstructural analysis on post-formed material are reported and a model offering some insight into possible deformation processes is presented. This model incorporated the effects of dynamic grain growth and cavitation within the material, which helped explain the superplastic response of 5083Al under complex straining cycle. Part II of this study is an investigation into possible methods of controlling deformation rate in superplastic alloys such as 5083Al in uniaxial tension. First, the variations in strain rate during constant crosshead-speed tensile tests were investigated. Following this, an examination of strain gradients within tensile specimens was performed and end effects, such as grip straining, were quantified. Modeling of tensile deformation was performed to obtain a better control of crosshead speed in an effort to achieve constant strain-rate tests. Lastly, a device was designed and constructed that allows for monitoring and controlling true local strain rate in specimen gauge regions during superplastic forming by measuring specimen width contraction. Constant strain-rate tests were achieved with this device, and the true hardening behavior of the material was revealed. The final part of this work is an investigation of texture development and hardening behavior during cold-rolling of a typical hot-rolled low-carbon steel. Plane-strain compression tests were used to simulate the rolling process and to quantify the hardening characteristics. Metallographic analysis of compressed material was performed to study the effects of cold rolling on the material's grain structure. Finally, the development of a crystallographic texture was examined with x-ray diffraction pole figures of the deformed material.